I. Field of the Invention
This invention relates generally to medical apparatus for the long-term delivery of medicaments to a desired release site within the body, and more particularly to an implantable drug delivery system which is electrochemical in nature and contains no moving parts.
II. Discussion of the Prior Art
In the treatment of certain diseases, it is desirable to administer various drugs to predetermined points within the body where the drug is effective in treating the disease process, but without burdening the rest of the body. For example, in the treatment of certain cancers, chemotherapy may be effective in killing the cancer cells but those same drugs may have serious effects on normal cells as well. Thus, they cannot be administered by way of a bolus injection into the vascular system and with reliance upon the blood circulation to carry the drug to the cancer site. In another example, certain drugs are effective in treating cardiac arrhythmias and it is desirable to deliver those drugs directly to the heart while minimizing or completely eliminating undesirable side effects. An effective drug pump is also invaluable to diabetics who must have one or more injections daily of insulin. The need to carry around a kit and to inject oneself with a hypodermic needle on this frequent basis is unpleasant at best and leads to problems with patient compliance.
The foregoing problems have been addressed by the prior art and, in this regard, reference is made to the Fischell U.S. Pat. No. 4,373,527 and the Blackshear et al U.S. Pat. No. 3,731,681. Each of these patents describes an implantable pump having a reservoir for storing a quantity of a liquid drug adequate to satisfy the patient's needs over a relatively long time period.
The Blackshear pump includes a housing divided into two fluid-type chambers with a pressurized bellows acting as the divider. The pump's outlet is coupled by tubing leading to the infusion site. In addition to requiring moving parts, the capillary tube used to dispense the drug at the treatment site is subject to becoming plugged by tissue ingrowth and blood clotting. The device of the Fischell U.S. Pat. No. 4,373,527 incorporates a battery-powered pulsatile pump having inlet and outlet valves and a ceramic filter is employed to filter out contaminants from entering the pump structure. However, there does not appear to be anything to prevent the buildup of clotting materials and/or tissue ingrowth into the outlet port 220 which would ultimately block the flow of medicament from the pump.